"Saw," the directing debut of James Wan, is a morose and frequently grisly low-budget horror item. The film casts a downbeat, unsettling pall over the proceedingsthe one genre where these are exclusively positive traitsbut as efficiently moody as the mise-en-scene is, the picture is just as inept in the plotting department. The screenplay by Wan and Leigh Whannell (also making his acting debut) is not an example of well thought-out storytelling, its several initial novel ideas eroded all the more by a meandering narrative and a blood-drenched, far-fetched climax that makes diminishing sense the more the viewer thinks about it.

For a while, "Saw" appears as if it may have more to offer than the usual serial killer thriller. Well-off doctor Lawrence Gordon (Cary Elwes) and bohemian photographer Adam (Leigh Whannell), complete strangers, awaken ramshackled on opposite sides of a decrepit, closed-off room with no recollection of how they got there and a dead body laying between them. Each find an envelope in their pocket, containing a tiny audio tape that, when played, spells out the enigmatic Jigsaw Killer's twisted plan. With Lawrence's wife, Alison (Monica Potter), and daughter, Maria (Makenzie Vega), being held hostage, he has only eight hours to set himself free and murder Adam. If he fails, his family will die and they will be left to starve and rot.

The plot hook "Saw" embraces immediately raises the film above the mediocre level of two recent movies about serial killersthe forgettable "Taking Lives" and laughably dreadful "Twisted." The Jigsaw Killer, as he is nicknamed and whom Lawrence was falsely suspected of being five months earlier, has never actually killed anyone, instead placing his victims in diabolical situations so compromising and maddening that it leads them to kill themselves. It is but an elaborate game for the Jigsaw Killer, and Lawrence and Adam have the dubious honor of being his latest unwilling participants. So far, so good, but director James Wan still appears too wet behind the ears to do his wickedly clever setup justice.

The narrative is schizophrenic, and, if not incomprehensible, certainly muddled, as "Saw" leaves its enthralling central story threadthe predicament of desperate captives Lawrence and Adamtoo often to pile on flashback upon flashback, sometimes flashbacks within flashbacks, and superfluous characters whose only purpose is to be red herrings for the killer's identity. In its non-linear approach, "Saw" reminds of the recent, superior "The Grudge," minus the tightly woven scripting that articulately brings all of its pieces together. In a key subplot that plays like a run-of-the-mill police investigation, detectives David Tapp (Danny Glover) and Steven Sing (Ken Leung) are lukewarm on the trail of Jigsaw, even as they are offered a few moments to look suspicious themselves. Too much wasted time is spent on these characters, particularly David Tapp, slowing down the pacing and uninvolving the viewer in Lawrence and Adam's dire straits. Meanwhile, the mystery aspect of the story is hopeless, as the eventual identity of the killer is one that no one could guess because the film doesn't play fair under the guidelines of a true whodunit. This is one case where pondering the movie's twists for even a few seconds will expose holes the size of Texas in its grand design.

The performances waver between passably committed to painfully amateurish, with character actor Cary Elwes (2004's "Ella Enchanted") and first-timer Leigh Whannell unevenly leading the way. Danny Glover (2004's "The Cookout") brings a respectable authority to his role of Detective David Tapp, even if he is above the material, while Monica Potter (2001's "Along Came a Spider") and Makenzie Vega (2000's "The Family Man") are effective in the draining but thankless parts of Lawrence's in-danger wife and daughter. And, as the only kidnapped person to solve Jigsaw's game and survive the ordeal, Shawnee Smith (2004's "A Slipping-Down Life") makes a riveting, if brief, appearance.

"Saw" can attest to putting the viewer on edgehow could a movie not that is as graphic as this one is?but, save for a nerve-racking sequence lit solely by a sparse camera flash, it doesn't know the first thing about creating suspense or jump scenes. With the killer seldom using a puppet to speak for itself, a freaky idea without a payoff or a point, the film is an example of clear ambition marred by inexperience. The ending is particularly a letdown, anticlimactic and lazily developed. For a similar, far more disturbing and assured feature also carrying the style-over-substance banner, 2002's underrated "FearDotCom" could run circles around this latest effort. "Saw" simply doesn't cut it.